This application relates to optical fiber devices and lasers.
The output frequency of a laser can drift or fluctuate due to various internal processes (e.g., shot noise and other fluctuations) or environmental factors (e.g., a change in temperature or vibrations). The frequency of a semiconductor laser, for example, can change with the electric driving current and temperature. Such variations in the laser frequency are undesirable in certain applications where the frequency stability is required.
For example, wavelength-division-multiplexing (WDM) has been used to expand the capacity of a fiber communication link by simultaneously transmitting different optical waves at different wavelengths. It is critically important to specify and standardize the wavelengths in WDM signals so that WDM devices, modules, and subsystems from different manufactures are compatible and can be integrated and deployed in commercial WDM networks. One commonly-used WDM wavelength standard is the International Telecommunication Union (ITU) standard, where the WDM wavelengths of different optical waves are required to match ITU grid frequencies. Hence, the laser transmitters for the different WDM channels need be stabilized against wavelength instability caused by either internal or external fluctuations.
Other applications, such as precision spectroscopic measurements and nonlinear optical processes, may also require frequency stabilization of lasers.
This application includes techniques and devices that use optical fibers and fiber devices to stabilize the frequency of a laser.